Staphylococcus aureus was discovered in 1879 and 100 years later the basis for its pathogenicity is not understood. Although S. aureus elaborates numerous toxins, enzymes and other antigens and although these undoubtedly contribute to the pathology observed in staphylococcal disease, it is not clear that any of them individually or collectively are responsible for the initiation of infection. As a general rule, staphylococci, in sharp contrast to other pyogenic cocci, are not normally encapsulated. However, in recent years several stable encapsulated strains of staphylococci have been isolated. These strains have the property of being lethal to mice, a property not possessed by nonencapsulated strains. Antibodies specific for the capsular polysaccharides protect the mice against an otherwise lethal challenge of the encapsulated staphylococcus. The capsules of three such strains, Smith diffuse, T, and M have been reasonably well-characterized, the last one (M) by this laboratory. Components of the capsules observed thus far are aminohexuronic acids, methyl pentosamines and amino acids. The research proposes to isolate and characterize, both chemically and biologically, several staphylococcal capsular polysaccharides. Specifically the capsular polysaccharides of S. aureus strains Smith diffuse, M, T, 7007, NS41D and NS58D will be isolated and the repeating sequences of each established as to linkage and anomeric configuration. The immunological characteristics of each will be investigated with a view of developing a staphylococcal vaccine for populations at high risk.